Method for preparing block copolymers of propylene

Abstract

An improved method for preparing block copolymers of propylene which comprises providing a polymerizer composed of at least two reaction vessels connected to one another, substantially homopolymerizing propylene in a first step and then copolymerizing ethylene and propylene in a second step in the presence of a stereoregular catalyst, characterized by carrying out the homopolymerization of propylene in the polymerizer composed of at least two reaction vessels connected to one another in series, then introducing the resulting polymer slurry into a countercurrent washing column and countercurrently washing the slurry with propylene, introducing the washed slurry withdrawn from the lower part of the washing column into a reaction vessel in the second step connected to the washing column and performing the polymerization of ethylene and propylene, of which ratio ranges from 15/85 to 95/5. According to this method, a block copolymer of propylene exhibiting excellent physical properties can be obtained efficiently.

What is claimed is: 
     
       1. A method for preparing block copolymers of propylene which comprises a first step of substantially homopolymerizing propylene in the presence of a catalyst in a polymerizer composed of at least two reaction vessels connected to one another in series so as to form a polymer slurry wherein said homopolymerization is conducted by bulk polymerization with propylene as a polymerization medium, introducing the polymer slurry into a countercurrent type washing column and countercurrently washing the slurry with pure propylene so as to remove catalyst from the polymer slurry, introducing the wash liquid of propylene withdrawn from the upper part of the washing column into the reaction vessel of the first step, introducing the washed polymer slurry withdrawn from the lower part of the washing column into a polymerizer and in a second step, performing copolymerization of ethylene and propylene of which the weight ratio ranges from 15/85 to 95/5 in the presence of a stereoregular catalyst and wherein at least one of an electron donating compound and an organoaluminum compound is added to the polymerizer of the second step. 
     
     
       2. The method for preparing block copolymers of propylene according to claim 1 wherein the polymerization in the second step is alternately, batchwise carried out in at least two reaction vessels connected to the countercurrent washing column in parallel. 
     
     
       3. The method for preparing block copolymers of propylene according to claim 1 wherein the polymerization in the second step is continuously carried out in at least two reaction vessels connected to the countercurrent washing column in series.